An oxide superconducting material comprising a single-crystal formed REBa2Cu3O7−x (RE means rare earth element) phase in which a RE2BaCuO5 phase is dispersed has a high critical current density (below, also indicated as “Jc”), so is magnetized by cooling in a magnetic field or by pulse magnetization and can be used as a superconducting bulk magnet able to generate a strong magnetic field.
A superconducting bulk magnet has the excellent feature of being able to generate an extremely powerful magnetic field in a compact space, but since an extremely strong magnetic field is sealed in the compact space, a large electromagnetic stress acts inside an oxide superconducting bulk material. This electromagnetic stress acts so that the sealed-in magnetic field spreads, so is also called “hoop stress”. In the case of a 5 to 10T class strong magnetic field, the electromagnetic stress which acts sometimes exceeds the mechanical strength of the material of the superconducting bulk material itself. As a result, the oxide superconducting bulk material is liable to break. If the oxide superconducting bulk material breaks, the superconducting bulk material can no longer generate a strong magnetic field.
If possible to prevent breakage of a superconducting bulk material by electromagnetic stress, the features of a superconducting bulk magnet of compactness and a strong magnetic field can be expected to be made use of for help in improving the performance of the equipment and reducing the size and lightening the weight of equipment in applications utilizing magnets such as marine motors or windpower generators or magnetic separation.
To prevent breakage of an oxide superconducting bulk material by electromagnetic stress, for example, PLT 1 proposes a superconducting bulk magnet configured by circular columnar shaped oxide superconducting bulk material and a metal ring surrounding the same. By configuring the magnet in this way, at the time of cooling, a compressive stress due to the metal ring is applied to the oxide superconducting bulk material. This compressive stress has the effect of reducing the electromagnetic stress, so it is possible to suppress breakage of the oxide superconducting bulk material.
Further, PLT 2 discloses a superconducting bulk magnet reinforcing the entire side surface of the superconducting bulk material by a metal ring etc. and, furthermore, reinforcing the top and bottom surfaces of the superconducting bulk material as well by reinforcing members. By configuring the magnet in this way, it becomes possible to generate a high magnetic field even in the case of a large superconducting bulk material.
In this regard, in general, a single-crystal formed oxide superconducting material is small in size. It is difficult to apply a superconducting bulk material obtained by working this to systems requiring generation of magnetic fields over relatively large areas (for example, large size rotating equipment, large size magnets, etc.). Therefore, it is necessary to assemble a plurality of superconducting bulk materials to form a single assembly of superconducting bulk materials and generate a magnetic field over a relatively large area.
In this regard, the above PLTs 1 and 2 only show that it is possible to prevent breakage of a single circular columnar shaped oxide superconducting bulk material and does not disclose a configuration comprising a plurality of superconducting bulk materials combined.
Regarding a configuration comprising a plurality of superconducting bulk materials combined, for example, FIG. 3 of PLT 3 discloses a superconducting magnetic field generating device which is manufactured by combining seven hexagonal shaped superconducting bulk materials, arranging a reinforcing member comprising a fiber reinforced resin etc. around them, and further arranging a support member comprising stainless steel, aluminum or other metal at outer circumference thereof.
Further, PLT 4 discloses an oxide superconducting bulk magnet comprising a superconducting bulk magnet having a through path and the circumference of the superconducting bulk magnet is covered by a high strength material. In particular, it discloses a superconducting bulk magnet comprising a plurality of bulk high temperature superconducting members having rectangular outer circumferences and inner circumferences which are respectively covered by rectangular high strength materials for supporting the outer circumferences.
Furthermore, PLT 5 discloses a superconducting magnetic device comprising a plurality of high temperature superconducting member cells bonded together by a binder to form a single compact superconducting cell assembly in which insulators or high electrical resistance materials (stainless steel, copper, or nickel) are interposed between adjoining high temperature superconducting cells. In particular, PLT 5 discloses a superconducting magnet device comprising rectangular shaped high temperature oxide superconducting bulk materials having the outer circumferences of which reinforcing members are covered or coated (PLT 5, Specification, paragraph 0009 and FIG. 6).
Further, PLT 6 discloses a superconducting permanent magnetic device having magnetic poles comprising a plurality of superconducting bulk materials arranged in parallel.